This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application entitled An Apparatus for Generating Composite vertical Synchronous Signal filed with the Korean Industrial Property office on Jul. 12, 1997 and there duly assigned Serial No. 97-32392 by that Office.
1. Field of the Invention
The present invention relates to display devices and, more particularly, to a device for generating sync signals for an externally applied composite video signal, which separates and processes and signals from the luminance signal contained in a composite signal input to a monitor.
2. Description of the Related Art
Recently developed multimedia-type computer systems provide a wide variety of display functions by including auxiliary equipment such as MPEG boards and television receiver cards. Along with this trend, a display monitor must also become capable of processing various signals by providing a function for processing a composite video signal which does not originate from the host computer.
A conventional display monitor having such a composite video function is shown in FIG. 1. FIG. 1 shows a host computer 100 including a CPU 110 for executing an application program and generating video data, and a video card 120 for processing the video data and outputting horizontal and vertical sync signals and an RGB signal.
Referring to FIG. 7, the display monitor includes a digital computer filter 210 for separating a composite signal externally applied thereto into a luminance signal (Y) and a chrominance signal (C); horizontal and vertical sync signal generators 221 and 222 for generating horizontal and vertical sync signals, respectively, based on the separated luminance signal output; a composite signal analyzing and horizontal/vertical oscillating circuit 250 for outputting an RGB video signal; a microcomputer 230 for determining display resolution based on sensed sync signal inputs from a sync signal switching circuit 223 in order to output a control signal to a synchronization circuit 240, and for generating select signals based on the application program; a video signal switching circuit 260 for selectively outputting the externally applied video signal or the video signal applied from the video card 120 according to the microcomputer""s video select signal, for amplification and display via a video amplifier 270 and a CRT 280, and the sync signal switching circuit 223 for selectively outputting the sync signals generated based on the externally applied composite video signal or those applied from the video card 120 according to the microcomputer""s sync select signal, for input to the microcomputer""s frequency discrimination circuitry (not shown).
As shown in FIG. 2, which is a more detailed circuit diagram of the operative elements of the above conventional display monitor, the separated luminance signal is applied to the horizontal sync signal generator 221 and is used to generate both the horizontal and vertical sync signals. That is, the luminance signal output from the digital computer filter 210 is applied to the base of a transistor Q1 via resistors R1 and R13 and a capacitor C1. The translator Q1 is turned on in response to the luminance signal, generating a composite horizontal sync signal across a load resistor R2. For a standard VGA monitor, this frequency is 15.75 kHz. The composite horizontal sync signal fed to the vertical sync signal generator 222 is integrated through resistors R3 and R4 and capacitors C4 and C5, so as to apply the vertical sync frequency (e.g., 60 Hz) to the case of a transistor Q2. A transistor Q3 is part of a Darlington pair formed with the transistor Q2 and configured with a resistor R5, to thereby generate the composite vertical sync signal across an output resistor R14.
Thus, the composite horizontal and vertical sync signals are applied to the sync signal switching circuit 223, together with the corresponding sync signals from the host computer 100, for selective application to the microcomputer 230. Meanwhile, the composite signal analyzing and horizontal/vertical oscillating circuit 250 regenerates the composite RGB video signal for output to the video signal switching circuit 250, together with the corresponding RGB video signal from the host computer 100, for selective application to the video amplifier 270 and ultimate display via the CRT 280 under the control of the synchronization circuit 240.
In the operation of the conventional display monitor having the above construction, a composite signal source such as a VCR or television tuner (not shown) is applied to the digital computer filter 210. The separated luminance signal output is used to create both sync signals via the horizontal and vertical sync signal generators 221 and 222.
Therefore, in the conventional display monitor as described above, the composite signal generated from a VCR or television may undergo mode conversions which temporarily render the composite video input without a luminance signal, such as between the recorded and unrecorded portions of a video tape or during the tuning of the television receiver. At this time, the conventional use of an externally applied composite sync signal causes a xe2x80x9cfree-runningxe2x80x9d display phenomenon, which generates an undesirable display including video noise, since no sync signal (either horizontal or vertical) input can be present for transmission to the display monitor via the microcomputer.
Accordingly, in order to overcome such drawbacks in the conventional art, it is therefore an object of the present invention to provide a device for generating the sync signals of a composite video signal, in which a horizontal or vertical sync signals input to the microcomputer are constantly maintained regardless of the state of a composite video signal source.
It is another object of the present invention to provide a device for generating the sync signals of a composite video signal, in which a free-running display phenomenon can be avoided.
It is yet another object of the present invention to provide a device fox generating the sync signals of a composite video signal, in which video display noise is reduced.
To achieve these and other objects and advantages and in accordance with the purpose of the present invention, as embodied and broadly described, there is provided a device for generating sync signals of a composite signal, including a microcomputer for generating a sync select signal based on display mode; a composite signal analyzing and horizontal/vertical oscillating circuit for generating horizontal and vertical oscillating signals based on a luminance signal separated from a composite signal input; a horizontal sync signal generator for processing the horizontal oscillating signal generated from the composite signal analyzing and horizontal,/vertical oscillating circuit so as to generate a composite horizontal sync signal; a vertical sync signal generator for processing the vertical oscillating signal generated from the composite signal analyzing and horizontal/vertical oscillating circuit so as to generate a composite vertical sync signal; and a sync signal switching circuit for selectively outputting one pair among the composite horizontal and vertical sync signals respectively generated from the horizontal and vertical sync signal generators and horizontal and vertical sync signals transmitted from a host computer, in response to the select signal generated by the microcomputer.